BEopt ASHP/MSHP minimum operating temperatures

I understand that the original default ASHP models were set to 0 F minimum ODB because, at the time, E+ couldn't handle anything below -4 F. That problem has since been fixed, and if the heat pump is based on, say, a mitsubishi zuba-central, it can actually operate down to -22 F (-30 C). My, concern is that the only input value in the model indicating performance levels below 47 F is the HSPF value, but that is based on AHRI testing at temperatures only down to 17 F. Is there any way to find out which heat pumps these models are based on so they can be adjusted properly? (The paper Eric shared is helpful but does not list heat pump manufacturers/model#, and I cannot determine the model# for ASHP in either AHRI or NEEP databases from BEopt inputs alone)link text

My other concern is about the MSHP models, whose capacity and performance is well defined thanks to the capacity retention fraction, but which does not appear to have a minimum operating temperature. Does the model simply extrapolate capacity below the capacity retention temperature until COP=1?

1 Answer

ASHP: I believe the BEopt options are meant to be generic. However, the BEopt variable speed ASHP may be based on something similar to the Nordyne iQ Drive or Carrier Infinity with Greenspeed.

MSHP: Yes, the capacity degradation is linearly extrapolated below the capacity retention temperature. COP is not involved in that extrapolation. My understanding is that most "cold climate" MSHP units do not actually have a compressor lock out temperature and people have observed them continuing to output heat even below the manufacturer specified minimum temperatures (typically -13 F or -15 F).